1. Field of the Invention
The present invention relates to a lens barrel and an image pickup apparatus.
2. Description of the Related Art
A lens barrel mounted on an image pickup apparatus, such as a single-lens reflex camera, includes a mechanism configured to move a lens holding frame that holds a lens, in an optical axis direction. For example, Japanese Patent Laid-Open Application No. (“JP”) 2009-251265 arranges, via balls, a first holder at one end of a cam cylinder configured to move the lens holding frame in the optical axis direction, and a force unit, a ring, balls, and a second holder at the other end of the cam cylinder. The cam cylinder, the force unit, and the ring are rotatable relative to the first holder.
However, according to JP 2009-251265, the force unit and the ring that relays the force applied by the force unit rotate with the cam cylinder, a large driving load (inertia moment) is applied when the lens holding frame is driven in the optical axis direction. As a result, when the driving force is constant, the acceleration or deceleration needs a long time and a long driving time period is necessary. Alternatively, a larger consumption power is necessary when a driving time period is constant.